Image forming apparatus

Abstract

An image forming apparatus includes an optical detecting device; a movable unit including a rotatable member having a first light-blocking surface and a second light-blocking surface; and a control unit. The movable unit rotates with rotation of the rotatable member so that the second light-blocking surface is movable to a first position where the optical detecting device is light-blocked and a second position where the optical detecting device is not light-blocked, and includes a locking member for locking the second light-blocking surface in the second position. When the first and second light-blocking surfaces pass through a detecting portion of the optical detecting device, the control unit discriminates a state of the movable unit on the basis of a detection result of the optical detecting device.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 an optical detecting device mounted in a main assembly of said image forming apparatus; 
 a movable unit, detachably mountable to the main assembly, including a rotatable member having a first light-blocking surface for blocking light and a second light-blocking surface different from the first light-blocking surface in length of a light-blocking region of said rotatable member with respect to a rotational direction of said rotatable member; and 
 a control unit, 
 wherein said movable unit rotates with rotation of said rotatable member so that the second light-blocking surface is movable to a first position where said optical detecting device is light-blocked and a second position where said optical detecting device is not light-blocked, and includes a locking member for locking the second light-blocking surface so that the second light-blocking surface moved to the second position is maintained in the second position, and 
 wherein when the first light-blocking surface and the second light-blocking surface pass through a detecting portion of said optical detecting device by the rotation of said rotatable member, said control unit discriminates a state of said movable unit on the basis of a detection result of said optical detecting device. 
 
     
     
       2. An image forming apparatus according to  claim 1 , wherein with respect to the rotational direction of said rotatable member, the length of the light-blocking region of the second light-blocking surface is shorter than the length of the light-blocking region of the first light-blocking surface. 
     
     
       3. An image forming apparatus according to  claim 2 , wherein said control unit discriminates whether or not which one of the first light-blocking surface and the second light-blocking surface passes through the detecting portion on the basis of the detection result of said optical detecting device. 
     
     
       4. An image forming apparatus according to  claim 1 , wherein said locking member is mounted on said rotatable member so as to be movable in the rotational direction of said rotatable member, and a rotation center of said locking member is the same as a rotation center of said rotatable member. 
     
     
       5. An image forming apparatus according to  claim 1 , wherein said optical detecting device includes a photo-interruptor. 
     
     
       6. An image forming apparatus according to  claim 1 , further comprising a movable light-blocking member including the second light-blocking surface and movable relative to said rotatable member. 
     
     
       7. An image forming apparatus according to  claim 6 , wherein said movable light-blocking member rotates integrally with said rotatable member, and when the second light-blocking surface is moved to the second position by a cam member, the second light-blocking surface is retracted from the first position toward a rotation center of said rotatable member. 
     
     
       8. An image forming apparatus according to  claim 1 , further comprising a plurality of image bearing members, wherein said movable unit includes an endless belt and a plurality of contact members contactable to an inner peripheral surface of the belt so as to cause the belt and the plurality of image bearing members to contact each other. 
     
     
       9. An image forming apparatus according to  claim 8 , wherein said control unit is capable of executing an operation in a first mode in which the plurality of contact members contact the belt and an operation in a second mode in which one of the plurality of contact members contacts the belt, and
 wherein when said control unit executes the operation in the second mode, the first light-blocking surface is positioned at the detecting portion of said optical detecting device. 
 
     
     
       10. An image forming apparatus according to  claim 8 , wherein said control unit discriminates a contact state and a separation state of the plurality of contact members with respect to the belt. 
     
     
       11. An image forming apparatus according to  claim 8 , wherein said movable unit includes a slidable member for changing a state of the plurality of contact members with respect to the belt by moving the plurality of contact members and includes a cam for moving the slidable member. 
     
     
       12. An image forming apparatus according to  claim 8 , wherein a cam and said rotatable member integrally rotate. 
     
     
       13. An image forming apparatus according to  claim 1 , wherein when the second light-blocking surface passes through the detecting portion of said optical detecting device after the first light-blocking surface passes through the detecting portion, said control unit discriminates that said movable unit is in a new state on the basis of the detection result of said optical detecting device. 
     
     
       14. An image forming apparatus according to  claim 1 , wherein said movable unit has an acting surface for moving the second light-blocking surface to the second position by acting on the second light-blocking surface placed in the first position. 
     
     
       15. An image forming apparatus according to  claim 1 , wherein said movable unit includes a fixing roller and a pressing roller, and
 wherein said control unit discriminates whether or not the fixing roller and the pressing roller are in a press-contact state by said optical detecting device and the first light-blocking surface.